SCOTUS agreed to hear the case because the court has never ruled on how far a president can go into illegal activity to do his job.Everything a President does is not ultimately shielded from post-office civil prosecution, so this is all nonsense to me and SCOTUS will see through the argument completely
There is another reason why SCOTUS could be hearing this case. The Jan 4th case would have been ready for trial by June 1st and the Classified Document case trial date was tentatively set for Aug 1. Neither of these cases can proceed until after SCOTUS's ruling scheduled for early July. Since the two cases can not run concurrently at least one if not both will be delayed till next year. Delaying these cases till next year will avoid any constitutional crises if Trump is found guilty. If Trump wins the election he can stop the prosecution. If Trump loses, there would be no constitutional crisis regardless of the outcome.